If middle-class Americans can afford salmon in 20 years, they might get it through a process like this:

The salmon hatch in nurseries. Eventually they are transferred to open tanks. The fish spend their entire lives in enormous indoor tanks, brushing against the same water, which has been recycled again and again. Waste is used to keep the water nutrient-rich. Eventually they are harvested. The salmon have never seen an open river, nor, perhaps, the sun—they have spent their lives in warehouses hundreds of miles from the sea.

From those landlocked warehouses—there’s already one in West Virginia—their bodies travel to restaurants and cities and grocery stores and homes.

This process may sound unnatural, but it increasingly appears to be the most sustainable way to raise salmon. So announced the Monterey Bay Aquarium Seafood Watch—the definitive source on the the sustainability of aquaculture—earlier this fall.  

Atlantic salmon farmed in recirculating aquaculture systems is a ‘Best Choice’ for consumers,” says the aquarium’s website. “These on-land production systems separate the fish from the surrounding environment and the risk of environmental impacts from pollution, escapes, and diseases are all low.”

This kind of salmon isn’t widely available right now. But as Josh Schonwald reports at Time, there are a number of companies currently testing the technology and scaling it up. It's not a given that those companies will succeed—past efforts in the space haven’t always worked out. Local Ocean, a startup so widely renowned it appeared on the cover of that magazine in 2011, went bottom-up last year.

But if one of those companies can find a way to make indoor aquaculture sustainable and profitable, it might just wind up becoming a major player in how the world’s upper class eats. And regardless, the premise of giant warehouses full of salmon—grown much like hydroponic weed—is a reminder of just what demand will do. It’s an image of what’s just becoming industrially possible to produce, and what nature can no longer manage without human stewardship.

One of my favorite definitions of the concept of city comes from City of Flows, a history of how cities and water by Maira Kaika. Kaika, a professor at the University of Manchester, describes the modern city as a “polymorphous metabolic socio-environmental process that stretches from the immediate environment to the remotest corners of the globe.”

This unending city is always stretching its tendrils of production further and further. Warehoused salmon, being trucked from the West Virginian countryside to New York City, is a tendril that reminds us that often the processes which drive the city are especially metabolic.

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